Input: MT - add support for balanced slot assignment

Some devices are not fast enough to differentiate between a fast-moving
contact and a new contact. This problem cannot be fully resolved because
information is truly missing, but it is possible to safe-guard against
obvious mistakes by restricting movement with a maximum displacement.

The new problem formulation for dmax > 0 cannot benefit from the speedup
for positive definite matrices, but since the convergence is faster, the
result is about the same. For a handful of contacts, the latency difference
is truly negligible.

Suggested-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Tested-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Henrik Rydberg <rydberg@bitmath.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/include/linux/input/mt.h b/include/linux/input/mt.h
index f583ff639776..d7188de4db96 100644
--- a/include/linux/input/mt.h
+++ b/include/linux/input/mt.h
@@ -119,7 +119,8 @@ struct input_mt_pos {
 };
 
 int input_mt_assign_slots(struct input_dev *dev, int *slots,
-                          const struct input_mt_pos *pos, int num_pos);
+                          const struct input_mt_pos *pos, int num_pos,
+                          int dmax);
 
 int input_mt_get_slot_by_key(struct input_dev *dev, int key);